Leonard Lance was born in Easton, Pennsylvania, into a political family. His parents were Anne M. (née Anderson) and Wesley Leonard Lance, who was a State Senator.[4][5] His great-uncle, H. Kiefer Lance, was also active in New Jersey politics.

Leonard Lance served as the law clerk to the Warren County Court in 1977 and 1978. He was assistant counsel for county and municipal matters to Governor of New JerseyThomas Kean from 1983 to 1990. He was a member of the New Jersey Council on the Humanities during the Whitman Administration by appointment of the Governor.

In 1987, he first ran for the General Assembly. He lost the Republican primary, ranking third with 17% in New Jersey's 23rd District.[7] Lance was appointed to the New Jersey General Assembly in February 1991 when then-Assemblyman William E. Schluter was appointed to the New Jersey Senate upon the ascension of Dick Zimmer from the New Jersey Senate to the United States House of Representatives in January 1991. After redistricting, Lance ran for the newly redrawn 23rd District in 1991, and won the Republican primary. In the general election, he ranked second with 30%, winning a seat. Incumbent Republican State Assemblyman Chuck Haytaian ranked first in the district with 33%.[8] In 1993, Lance won re-election to a second term with 40%.[9] In 1995, he won re-election to a third term with 34%.[10] In 1997, he won re-election to a fourth term with 30%.[11] In 1999, he won re-election to a fifth term with 36%.[2]

After redistricting, he ran for the New Jersey Senate in 2001 in the 23rd District. He defeated Democrat Frederick P. Cook 69%–31%.[12] In 2003, he won re-election to a second term with 68%.[13] In 2007, he won re-election to a third term with 67%.[1]

In the general assembly, he served as the Chairman of the Appropriations Committee from 2000 to 2002 and the Vice Chairman of the Appropriations Committee, when it handled the state budget, from 1996 to 2000. While Appropriations Committee Chairman, the committee oversaw state finances, taxation and spending on individual legislation, while budget issues were passed to a separate Budget Committee.

He served on the Joint Budget Oversight Committee, the Legislative Services Commission and the Budget and Appropriations Committee.[6] As Republican Budget Officer, he served as the Ranking Minority Member of the Budget and Appropriations Committee, along with serving as the Republican Senate Caucus' chief point person on budget and finance issues and in budget negotiations.

On June 3, 2008, Lance won the Republican primary to replace retiring U.S. Congressman Mike Ferguson in the New Jersey's 7th congressional district with 40% of the vote, defeating six opponents: Kate Whitman, the daughter of former Governor Christine Todd Whitman, former Summit Common Council President P. Kelly Hatfield, Scotch Plains Mayor Martin Marks, veteran Tom Roughneen, activist Darren Young, and professor A.D. Amir.[15] The primary left his campaign's funds depleted, leading him to hold several fundraisers, including one with President George W. Bush. Touring his district, he ran on a platform of fiscal conservatism, moderate social values, and environmentalism. He vowed to be "an independent voice" in Congress if elected.

His Democratic opponent was Linda Stender, a New Jersey Assemblywoman who unsuccessfully challenged Republican incumbent Ferguson in 2006. During the campaign, Lance took strong positions against the Alternative Minimum Tax, the estate tax, Governor Jon Corzine's controversial toll hike plan, and the partisan nature of the United States Congress. He came under fire from Stender's campaign for his 2006 vote in the New Jersey Senate against a bill which prevented pharmacists from refusing to dispense medication such as birth control pills due to religious concerns. Lance was one of only a few Senators to vote against the bill. However, both Lance and Stender are pro-choice. Lance was firmly opposed to negotiations with Iran on the presidential level, saying that he only favors holding such talks on a ministerial level. He also made energy independence one of his signature issues, along with fiscal accountability and debt reduction. On foreign policy, both candidates supported withdrawal from Iraq, a two-state solution in the Israel-Palestine conflict, and increased attention to the genocide in Darfur. Lance and Stender debated each other twice during the campaign. In September, they met in Scotch Plains for a debate hosted at the Jewish Community Campus of Central New Jersey. It was moderated by Westfield Rabbi Douglas Sagal. The candidates met in October in Edison for a second debate, which was televised on News 12 New Jersey and moderated by Walt Kane. On October 21, The Star-Ledger editorial board endorsed Lance in the 2008 election. On October 25, The New York Times followed suit. Eight other newspapers also endorsed Lance over Stender.

On June 8, 2010, Lance defeated three other candidates in the 7th District Republican primary, two of whom claimed to be tea party activists. He received 56% of the vote with the rest of the vote split among: businessman David Larsen (31%), IT consultant Lon Hosford (8%), and real estate appraiser Bruce Baker (5%).[18][19]

Lance defeated the Democratic nominee, science teacher Ed Potosnak, in the November general election 59%–41%.[20]

Redistricting made Lance's district significantly more Republican than its predecessor.[21][22] The new map pushed the 7th to the north, absorbing several heavily Republican areas that had previously been in the strongly Republican 5th and 11th districts while losing some Democratic-leaning areas.

In the 2012 Republican primary, Lance was again challenged by Larsen, who identifies himself with the Tea Party movement although he is not formally a member.[23] On June 5, 2012, Lance again won the Republican primary, this time 61%–39%.[24] Lance defeated the Democratic challenger, Assemblyman Upendra J. Chivukula, 57%–40%.

In June 2009 Lance was one of only eight Republicans in the House of Representatives to break with their party and vote for the American Clean Energy and Security Act. Lance had campaigned as a strong advocate for environmental protection and reduction of American dependence on foreign oil. In supporting the bill, Lance cited the bill's economic benefits for New Jersey, the fact that it would not enlarge the national debt, estimates by the Energy Information Administration and Congressional Budget Office suggesting that costs to consumers would be minimal, and its goal of reducing American dependence on foreign oil.[25]

Lance is a co-chairman of the House Republican Israel Caucus. The caucus focuses on the relationship between the United States and Israel. It is one of the largest organizations of Members of Congress, in terms of membership numbers.[27] Lance has served as a co-chairman since at least 2011.[28] Additionally, Lance is a member the Congressional Israel Allies Caucus. The caucus is sponsored by the Israel Allies Foundation, a group that promotes communication between legislative members in different countries and supports the right of Israel to exist in peace.[29][30]

Lance also serves as the Republican chairman of the Rare Disease Caucus. The goal of the caucus is to get Members of Congress to support passing bills that help people who suffer from rare diseases.[31] Seventy-six Members of Congress are caucus members.[32]

In 2013, Lance introduced the Modernizing Our Drug and Diagnostic Evaluation and Regulatory Network Cures (MODDERN) Act, a bill intended to encourage new innovative treatments for a variety of diseases and ailments. The MODDERN Drug Act proposes to reevaluate and reintroduce drugs that were once in the development phase, back into production and testing. Backers of the bill hope this will lead to new treatments that were once thought too costly to research and test. This bill would benefit patients suffering from a variety of ailments including but not limited to: ALS, Parkinson's, cancer, autoimmune diseases, and Alzheimer's.[33]